1. Field of the Invention
The present invention relates to an improved cylinder-type air damper for use in, for example, glove boxes of automobiles.
2. Description of the Related Art
A conventional air damper of this type is disclosed in Japanese Utility Model Registration Publication No. 2557064.
The conventional air damper, not shown in a figure, comprises a tubular cylinder with both ends open, a piston movable in the cylinder, to which piston a base loop of a string is coupled, a valve device attached to one opening end of the cylinder to control the amount of air passage, a guide cap attached to the other opening end of the cylinder and having a guide wall for the string and a compression coil spring interposed between the guide cap and the piston in the cylinder to resiliently bias the piston in the direction of the one end of the cylinder.
When the air damper is used in a glove box of an automobile, the cylinder is fixed to an instrument panel side, and the top end of the string extending outward from the guide cap of the cylinder is fixed to a glove box side. When the glove box is moved in the opening direction, the string is gradually drawn out from the cylinder, and the piston moves in the same direction while compressing the compression coil spring against its resilient biasing force in the cylinder. At that time, air flows into the cylinder via the valve device, producing a dampening effect. This ensures that the glove box gradually moves to an opening state.
When the glove box is moved in the closing direction, the piston is forcefully pushed back with the string in the direction of the one end of the cylinder by the resilient biasing force of the compression coil spring, and the air accumulated in the cylinder is released via the valve device to the outside. As a result, the piston swiftly moves in the cylinder, promoting the closing motion of the glove box.
As described above, the conventional air damper has an advantage of ensuring smooth opening/closing motions of the glove box. However it has a fear of generation of impulsive sound at the time of full opening of the glove box due to a shortage of dampening effect when the glove box is upsized and weighs more, or moves close to the full opening position according to a geometrical location where the center of gravity of the glove box door moves beyond the top dead center of a pivot shaft in a direction to move away from the pivot shaft so that the moving speed of the glove box door rapidly increases due to acceleration or an increase of angular moment.
The present invention has been achieved with such points in mind.
It therefore is an object of the present invention to provide an air damper which can effectively solve the above-described problem of the conventional air damper.
To achieve the object, according to a first aspect of the present invention, there is provided an air damper comprising a tubular cylinder with a first opening end and a second opening end, a piston movable in the cylinder, a first coil spring resiliently biasing the piston in the cylinder in the direction of the first end of the cylinder, and a string for transferring a dampening effect produced by a motion of the piston to an openable object, a shaft with a flange slidably fitted into the piston and a second coil spring interposed between the flange of the shaft and the piston inside the first coil spring, the second coil spring exerting a resilient biasing force at later stages of the motion of the piston in the direction of the first opening end of the tubular cylinder.
Thus in the present invention, even when an openable object is upsized or moves close to the full opening position with a geometrical location where the center of gravity of an absorbed object (glove box door) moves beyond the top dead center of a pivot shaft in a direction to move away from the pivot shaft, the second coil spring exerts the resilient biasing force as well as the first coil spring does at later stages of the moving range of the piston. As a result, the fear of generation of impulsive sound at the time of full opening of the openable object due to a shortage of dampening effect can be surely prevented.
As a second aspect, a hook is preferably provided in the piston of the air damper according to the present invention for hooking a base loop of the string thereon, and a slit is preferably provided in both sides of the shaft between which the flange is sandwiched so as to pass the base loop of the string therethrough.
Thus in the present invention, when sliding into the piston, the shaft can be prevented from interfering with the base loop of the string, maintaining the slidable relationship with the piston.
As a third aspect, a tapered surface is preferably provided internally at an edge of the shaft of the air damper according to the present invention, and an abutment is preferably provided on a cap that is attached to the second opening end of the cylinder, the abutment abutting against the tapered surface.
Thus in the present invention, when the edge of the shaft abuts against the cap with a piston motion, the tapered surface formed internally at the edge abuts against the abutment of the cap, thereby elastically widening the edge of the shaft through slits. This structure absorbs shock and prevents the generation of striking sound.